The methane content in fuel gas in landfills decreases with increasing time in service. Currently, gas motor operation must be halted if the methane content drops below a minimum value of approximately 35 to 40%, which is the content necessary for combustion in the gas motor. As a consequence, the pollutant-rich landfill gas with methane content below the minimum value, can no longer be disposed of or utilized as a fuel for engines or motors. The landfill gas produced with low methane content must be burned at high temperature in a special flare in order to minimize the pollutant discharge. This holds true for all lean gases whose heating value lies below the minimum value required for operation with a gas motor.
Boosting of the heating value of lean gases by means of the admixture of rich gases, such as natural gas, is not practiced at present because known industrial gas mixing systems would require an excessively large investment.
German patent document DE-OS 15 76 321 describes an apparatus which allows operation of a gas motor with various gases having various heating values. Upon a change of gas heating value, the gas pressure is changed in inverse proportion to the heating value of the gas being fed to the gas motor. Use of such apparatus presupposes maintenance of a minimum heating value of the gases used. Mixing of the two types of gases occurs only briefly at the changeover of one gas to another gas.
German patent document DE-A 41 37 573 discloses a gas motor having a gas mixer designed as a venturi mixer with adjustable venturi body.